The Electromagnetic Spectrum (WJEC GCSE Physics: Combined Science)

• The electromagnetic spectrum (em) is a collection of waves that share the following properties:
  • They are all transverse
  • They can all travel through a vacuum
  • They all travel at the same speed in a vacuum
  • They all transfer energy
• There are 7 types of electromagnetic waves, which all together form a continuous spectrum
• The electromagnetic spectrum is arranged in a specific order based on the wavelengths or frequencies

The Electromagnetic Spectrum from Longest Wavelength to Shortest Wavelength

Visible light is just one small part of a much bigger spectrum: The electromagnetic spectrum

• The relationship between frequency and wavelength of waves across the electromagnetic spectrum is
  • The higher the frequency, the shorter the wavelength
  • The lower the frequency, the longer the wavelength
• This means that radio waves have a lower frequency, and a longer wavelength than UV waves
• This can be seen from the wave equation

• Where:
  •  = speed of the wave in metres per second (m/s)
  •  = frequency of the wave in hertz (Hz)
  •  = wavelength of the wave in metres (m)
• Since all electromagnetic waves travel at the speed of light in a vacuum, this is constant
  • Therefore, in the equation, in keeping v constant, if f increases then λ must decrease

Relationship Between Wavelength and Frequency

The larger the wavelength, the lower the frequency. The speed remains the same

• The higher the frequency, the higher the energy of the wave
• Waves with higher energy are:
  • Highly ionising
  • Harmful to cells and tissues causing cancer (e.g. UV, X-rays, Gamma rays)
  • For more information, see our revision note on Radiation

• Waves with lower energy are:
  • Useful for communications and they are used to transmit information, for example: 
    • Radio waves are used in long-range communications, such as for radio and television
    • Microwaves are used in mobile phones and satellite communications as they can penetrate the Earth's surface
    • Infra-red waves and visible light are used in optical fibres as they can undergo total internal reflection
  • Less harmful to humans